1. Field of the Invention
This invention relates to an automatic document feeder for automatically feeding given original documents one by one to the image reading station of an image processing device such as a copying machine and printer, and more particularly, to a compact and simple document feeder having a common document tray for placing thereon one or more original documents to be fed into the image processing device and receiving the documents sent out from the image processing device.
2. Description of the Prior Art
For coping with a need for downsizing image processing devices such as a copying machine, facsimile, image scanner, and printer, the latest automatic document feeders mounted on the image processing devices tend to be made compact without degrading the performance in handling and transporting the given original document. The copying machine typical of the image processing device generally has a transparent platen on which an image reading station is defined and one given original document is placed for being optically scanned to read an image on the document. On the platen, there is mounted the document feeder for automatically feeding and sending out the given original document to and from the image reading station defined on the platen.
The automatic document feeder usually comprises a document feeding tray for placing thereon the original documents to be fed hereafter one by one to the image reading station on the platen, and a document discharging tray for receiving the original documents sent out from the image reading station upon completion of image processing. For directly transporting the document to and from the image reading station, a document transporting unit is built into the document feeder and overlaid on the platen.
It has been so far attempted to place the document feeding tray and document discharging tray one upon another in order to reduce the area occupied by the document feeder. One illustrative instance of the document feeders of this kind is disclosed in U.S. Pat. No. 4,023,791 (corresp. to Japanese Pat. Publication No. SHO 60-657(B2).
In the document feeder proposed by said U.S. Patent, the document feeding tray is independently placed on and displaced horizontally from the document discharging tray to facilitate the removal of the discharged original documents from the document discharging tray, resulting in a large overall size of the document feeder. Furthermore, the proposed document feeder is likely to entail a disadvantage such that, when the document to be fed has the habit such as curvature, the leading end of the document sent out from the image processing device to the document discharging tray by the document transporting unit after image processing is possibly caught by the bottom of the document feeding tray.
A document feeder proposed by Japanese Patent Application Public Disclosure No. HEI 3-120125(A) has a document tray for placing a stack of original documents thereon. In this proposed feeder, the documents stacked on the document tray are drawn one by one and fed to an image reading station and sent back from the image reading station onto the top of the stack of documents left on the document tray in a U-turn. The documents sent back from the image reading station and the stack of documents still left on the document tray are divided by a pair of document receiving members. The document being discharged from the image processing station moves in the opposite direction to the direction in which the document left on the document tray is sent into the image reading station, while coming in sliding contact with the document stacked on the document tray from the leading end toward the tail end of the document. When discharging the document from the image reading station onto the unfed documents stacked on the document tray, there is a possibility that the leading end of the discharged document collides with the leading end of the the stack of documents left on the document tray, thus causing the discharged document to be obstructed by the stack of documents left on the document tray.
A document feeder of different type has been proposed, which has a common document tray serving as a document feeding tray for feeding documents to be fed to the image reading station in a copying machine and a document discharging tray for receiving the documents sent out from the image reading station. For instance, a recycling automatic document feeder (generally called "recycle-ADF") for circulating several times a plurality of original documents through a transporting passage including the image reading station to obtain a plurality of sets of copies is disclosed in Japanese Patent Application Public Disclosures Nos. SHO 55-98762(A) and SHO. 59-114249(A).
The document tray in the conventional recycle-ADF is formed by merely combining the document feeding tray and document discharging tray, so that the documents sent out from the image reading station of the copying machine each time the image processing is completed are put on the top of the unfed documents stacked on the document tray. To count the number of the circulation of the documents being subjected to image processing, a cycle counting lever is interposed between the documents to be fed to the image reading station and the discharged documents sent out from the image reading station.
In the conventional ADF described above, since the documents still left on the tray to be read and the discharged documents sent out from the image reading station are divided only by the simple counting lever, but not independently separated from each other, the discharged document possibly collides with the unfed documents stacked on the document tray, thus developing feeding trouble and causing the discharged documents to be out of order. This disadvantage becomes particularly conspicuous when the original documents different in size are dealt with.
If a partition member is used to prevent the unfed documents stacked on the document tray to be read from interfering with the advancing of the document discharged from the image reading station, the handling work of getting the documents in and out relative to the document tray becomes onerous.